1. Field of the Invention
The present invention relates to a CMP (Chemical Mechanical Polishing) pad used in chemically and mechanically polishing a work such as a semiconductor substrate (wafer), and a CMP processing apparatus using the same.
2. Description of Related Art
In a process of producing semiconductor devices, such a treatment is carried out that makes a wafer surface flat and smooth as required. The chemical and mechanical polishing (CMP) process has come to be regarded as a promising process for making a wafer surface smooth and flat.
A CMP processing apparatus comprises a polish head that rotates while holding a wafer, a polish pad disposed to face the polish head, a platen that holds the polish pad, and a slurry supply unit that supplies a polishing medium (slurry) including a chemical liquid and abrasive particles (made of alumina, for example) onto the polish pad. With this constitution, when a wafer is pressed against the polish pad while rotating the polish head, the surface of the wafer is chemically and mechanically polished by the actions of the chemical liquid and the abrasive particles. The platen is adapted to move along the wafer surface, so that the polishing operation is carried out while changing the contact position between the polish pad and the wafer.
The polish pad has such a laminated structure as, for example, a hard pad having a relatively high coefficient of elasticity is laminated on a soft pad having a relatively low coefficient of elasticity. The coefficient of elasticity with respect to compression in the direction of pressing against the wafer to be polished is uniform throughout the pad surface.
Another polish pad of such a configuration has been proposed as the so-called fixed abrasive particles type where abrasive particles are fixed onto the pad surface. In this case, it suffices to supply only a chemical liquid onto the polish pad. The polish pad of this constitution comprises abrasive particles of substantially the same size and the same shape disposed on the pad surface to be uniformly distributed thereon, with all abrasive particles making contact with the wafer under substantially the same condition.
With the polish pads described above, condition of contact with the work being polished is constant throughout the pad surface. Although this constitution has such an advantage that the surface of the work can be polished uniformly, it may not necessarily provide advantage at all times since only a certain fixed condition of polish can be achieved.
In case it is desired to polish roughly at a high polishing rate in an early stage of the polishing process and carry out fine polish in the last stage of the polishing process, for example, the polish pad must be changed in the course of the polishing process. In practice, it is required to transfer the wafer from one CMP processing apparatus to another CMP processing apparatus. This may result in more complex and larger production apparatus.